1. Field of the Invention
Described herein is a device relating to light engines for use in lighting fixtures, such as troffer-style fixtures, that are well suited for use with solid state lighting sources, such as light emitting diodes (LEDs).
2. Description of the Related Art
Troffer-style fixtures are ubiquitous in commercial office and industrial spaces throughout the world. In many instances these troffers house elongated fluorescent light bulbs that span the length of the troffer. Troffers can be mounted to or suspended from ceilings, and can be at least partially recessed into the ceiling, with the back side of the troffer protruding into the plenum area above the ceiling. Typically, elements of the troffer on the back side dissipate heat generated by the light source into the plenum where air can be circulated to facilitate the cooling mechanism. U.S. Pat. No. 5,823,663 to Bell, et al. and U.S. Pat. No. 6,210,025 to Schmidt, et al. are examples of typical troffer-style fixtures.
More recently, with the advent of the efficient solid state lighting sources, troffers have been developed that utilize LEDs as their light source. The LEDs can be arranged in different ways in the troffers, with some having LEDs arranged in a light engine. LEDs are solid state devices that convert electric energy to light and generally comprise one or more active regions of semiconductor material interposed between oppositely doped semiconductor layers. When a bias is applied across the doped layers, holes and electrons are injected into the active region where they recombine to generate light. Light is produced in the active region and emitted from surfaces of the LED.
LEDs have certain characteristics that make them desirable for many lighting applications, such as troffers, that were previously the realm of incandescent or fluorescent lights. Incandescent lights are very energy-inefficient light sources with approximately ninety percent of the electricity they consume being released as heat rather than light. Fluorescent light bulbs are more energy efficient than incandescent light bulbs by a factor of about 10, but are still relatively inefficient. LEDs by contrast, can emit the same luminous flux as incandescent and fluorescent lights using a fraction of the energy.
In addition, LEDs can have a significantly longer operational lifetime. Incandescent light bulbs have relatively short lifetimes, with some having a lifetime in the range of about 750-1000 hours. Fluorescent bulbs can also have lifetimes longer than incandescent bulbs such as in the range of approximately 10,000-20,000 hours, but provide less desirable color reproduction. In comparison, LEDs can have lifetimes between 50,000 and 70,000 hours. The increased efficiency and extended lifetime of LEDs is attractive to many lighting suppliers and has resulted in their LED lights being used in place of conventional lighting in many different applications. It is predicted that further improvements will result in their general acceptance in more and more lighting applications. An increase in the adoption of LEDs in place of incandescent or fluorescent lighting would result in increased lighting efficiency and significant energy saving.
Light engines that can be utilized in lighting fixtures, such as those mentioned above, typically comprise various components such as an array of multiple LED packages mounted to a printed circuit board (PCB), substrate or submount. The array of LED packages can comprise groups of LED packages emitting different colors, and specular or diffuse reflector systems to reflect light emitted by the LED chips. Some of these LED components are arranged to produce a white light combination of the light emitted by the different LED chips.
Modern lighting applications often demand high power LEDs for increased brightness. High power LEDs can draw large currents, generating significant amounts of heat that must be managed. In addition to the above mentioned components, many systems utilize heat sinks which must be in good thermal contact with the heat-generating light sources. Some previous LED based light engines would have inadequate thermal management means, resulting in unacceptable heating of the light engine and/or heat related failure of the light engine. For most current lighting applications, light engines utilize heat sinks to adequately dissipate heat from the light sources into the ambient. Troffer-style fixtures generally dissipate heat from the back side of the light engine or the fixture that extends into the plenum. This can present challenges as plenum space decreases in modern structures. In addition to thermal management, heat sinks often provide necessary structural stability for light engines.
As mentioned above, many light engines utilize components such as PCBs, heat sinks, reflective elements and lenses, which are part of the light engine and are formed separately from the light engine body. These separately formed components must be assembled and/or attached to the light engine body to form a complete light engine. As the number of desirable or required components that must be later assembled increases, the manufacturing and assembly processes become more complicated, costly and requires more materials. This can result in a light engine that is not only complex, but also expensive.